Citation

Abstract / Synopsis

Weight reduction, fatigue resistance, vibration damping and design flexibility to meet critical vibration characteristics are offered by substituting fibrous composites for conventional metals in power transmission shafts, which utilized in many applications including automotive. Strongly related to stiffness, the optimal design constrained by rotational frequency, torsional frequency and applied torque, which are to be traversed by increasing the critical speed, torsional stiffness and critical torque, respectively. However, composite drive shaft (DS) design is a problem of prescribed stiffness with the variables of layers material, thickness and stacking. Least cost can be achieved by using a hybrid of carbon/epoxy and E-glass/epoxy as carbon fibers with their higher specific stiffness, have comparatively high price. The main objectives are to study the effect of fiber orientation angles and stacking sequence on the natural frequency, buckling strength and fatigue life. Besides, the study of the torsional stiffness and failure modes of composite tubes, are included in the objectives.
Finite element analysis (FEA) software has been used to predict the fatigue life of composite (DS) after linear dynamic analysis for different stacking sequence. Eigenvalue analysis used to investigate the effect of two design variables, namely the fiber orientation angle and layers stacking sequence on the bending natural frequency and buckling torque. Results from the numerically developed models are validated by solutions obtained from a close-form analysis of the DS. Experimental study on scaled woven fabric composite models was carried out to investigate the torsional stiffness.
Based on FEA results, it was found that the natural frequency increases with decreasing fibers angles. The DS has a reduction equal to 54.3% of its frequency when the orientation angle of carbon fibers at one layer, among other three glass ones, transformed from 0º to 90º. On the other hand, the critical buckling torque has a peak value at 90º and lowest at a range of 20º to 40º when the angle of one or two layers in a hybrid or all layers in non-hybrid changed in sameness. The layers stacking sequence has no effect on the critical speed (natural frequency) of DS but significantly affect buckling torque and fatigue resistance. In the investigated design, the best stacking sequence gave a buckling torque of 2303.1 Nm, while the worst gave 1242 Nm with a loss of 46.07%. Concerning the buckling, the measuring factor for the goodness of stacking sequence is a component in the bending stiffness matrix [D]. This component D22 is the normal bending stiffness along the hoop direction. Therefore, D22 specify the ability of DS material to deflect in radial direction or to (buckle). In addition, the coupling between twist moment and normal curvature appears as D16 and D26 components, has a substantial effect on both the buckling torque and natural frequency. Concerning fatigue, longer life of DS realized by locating ±45º layers together and inner mostly while locating 0º/90º layers together with 90º layer exposed to outside. Indeed, the stacking sequence of [±45,0,90] is the best for both fatigue and buckling resistance.
From the experimental work, composite tubes of fiber orientation angles of ±45º experience higher load carrying capacity and higher torsional stiffness. Specimens of carbon/epoxy or glass/epoxy composites with fiber orientation angles of ±45º show catastrophic failure mode. In a hybrid of both materials, carbon layers dominate the failure mode.